Synthesis of 3-Acyloxyindolenines by TiCl3-Mediated Reductive Cyclization of 2-(ortho-Nitroaryl)-Substituted Enol Esters.

In the presence of TiCl3, the reductive cyclization of tetrasubstituted enol esters bearing a 2-(ortho-nitroaryl) substituent affords 3-acyloxy-2,3-disubstituted indolenines in good yields. A domino process involving the partial reduction of nitro to a nitroso group followed by 5-center-6π-electrocyclization, 1,2-acyloxy migration, and the further reduction of the resulting nitrone intermediate accounts for the reaction outcome. The so-obtained indolenines are converted smoothly to 2,2-disubstituted oxindoles via a sequence of saponification and semipinacol rearrangement.

Tritylium assisted iodine catalysis for the synthesis of unsymmetrical triarylmethanes.

The combined Lewis acid catalytic system, generated from molecular iodine and tritylium tetrafluoroborate effectively catalyzed the Friedel-Crafts (FC) arylation of diarylmethyl sulfides providing an efficient access to various unsymmetrical triarylmethanes. The addition of tritylium and iodine created a more active catalytic system to promote the cleavage of sulfidic C-S bonds.

Visible-Light-Triggered C-C and C-N Bond Formation by C-S Bond Cleavage of Benzylic Thioethers.

The cleavage of sulfidic C-S bonds under visible-light irradiation was harnessed to generate carbocations under neutral conditions and synthesize valuable di- and triarylalkanes as well as benzyl amines. To this end, photoredox catalysis and direct photoinduced C-S bond cleavage are used as complementary approaches and participate in the versatility of the general strategy. Extensive mechanistic studies have demonstrated the diversity of the reaction mechanism at work in these different reactions.